I have found 3 anagrams for SIX HUNDRED THREESCORE AND SIX (Rev. 13:18).  They are as follows:

DNA HEX OR DIRTINESS HEX, CURSED, or OR DIRTINESS HEX AND CURSED HEX, or

TORRID SEX AND UNCHERISHED SEX are the 3 anagrams.

TO RECEIVE HARM, INHERIT A DARK THING, or HATER TO HARM, I RECEIVE IN DARK THING

are both anagrams for TO RECEIVE A MARK IN THEIR RIGHT HAND. (Rev. 13:16)

OR TO INFER HADES HEIR is an anagram for OR IN THEIR FOREHEADS. (Rev. 13:16)

OH, SULLY, DAMNING DEATH OVER BEAST, MAN THAT HATH THE MARK is an anagram for

AND THAT NO MAN MIGHT BUY OR SELL, SAVE HE THAT HAD THE MARK. (Rev. 13:17)

TREE OF BEHEMOTH SATAN, or THE SATAN FOE TOMB HERE or SATAN, FOE, HE BETROTH ME, or AFTER NOTE - BE HOT SHAME are all anagrams for OR THE NAME OF THE BEAST. (Rev. 13:17)

BE HUMAN HEIR OF MONSTER, or SHIAH MEMBER TURN ON FOE, or THRONE BE FROM SHIA MEN, or SHIA THRONE, NUMBER OF ME are all anagrams for OR THE NUMBER OF HIS NAME.

(Rev. 13.17)

BUT UNFETTERS A BEHEMOTH CON is an anagram for COUNT THE NUMBER OF THE BEAST. (Rev. 13:18)

I'M BRUTE SHIA FRONT MAN FOE, or OH, AM MEAN BRUTE FOR SIN FIT are anagrams for FOR IT IS THE NUMBER OF A MAN. (Rev. 13:18)

MANY IN WHORE, BASEST PATH is an anagram for ANY MAN WORSHIP THE BEAST. (Rev. 14:9)

HADES AIM OF HIS HEIR RECEIVING IN HADES DNA MARK, or HADES AIM AND OF HIS HEIR RECEIVING IN HADES MARK are both anagrams for AND HIS IMAGE AND RECEIVE HIS MARK IN HIS FOREHEAD. (Rev. 14:9)

HEIR OF HADES is an anagram for HIS FOREHEAD. (Rev. 14:9)

AH, I'M FROM THE SNAKE, or MARK OF THINE SHAME are both anagrams for THE MARK OF HIS NAME. (Rev. 14:11)

BE THAT FOE'S MARK, or THE FOE'S TAB MARK are both anagrams for MARK OF THE BEAST. (Rev. 16:2)

THAT MARK BE THE DECEIVER FOE'S is an anagram for RECEIVED THE MARK OF THE BEAST.

(Rev. 19:20)

If you reread I Corinthians 15:49-54, at the rapture of living believers and the resurrection of the dead in Christ, our DNA is miraculously changed in a twinkling of an eye from mortal, corruptible flesh and blood to immortal and incorruptible flesh like our Lord Jesus.  Since Satan is a imitator of God, I could see him possibly somehow incorporating either his DNA or the DNA of another fallen angel like Abaddon,who ascends out of the bottomless pit, or maybe even the DNA of the son of perdition into the mark of the beast so the person receiving it would be marked as Satan's forever and can never repent of their sins even if they wanted to. I don't know how Satan would accomplish this though, but it may be some eternal death cell.  Look what happened to Adam and Eve in the garden of Eden when they sinned.  Their sin brought all mankind death because the wages of sin is death so every human being dies unless they are raptured to heaven like Enoch when he was translated.

In any case while TO INFER HADES HEIR is an anagram for IN THEIR FOREHEADS, I also found that DOER'S FAITH HERE IN is also an anagram for IN THEIR FOREHEADS, but it is referring to those servants of God or the 144,000 who are sealed in their foreheads in Rev. 7:3, 14:1 and those in Rev. 22:4.